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Introductory Astronomy: Stellar Composition

The stellar spectrum is created by the emission and absorption of all of the different elements that make up a star. Each of these elements emits at certain wavelengths. When astronomers analyze the spectrum of a star, they use this fact to identify which elements are present in the star. Astronomers associate each spectral line in the star's spectrum with the element that is responsible for that line. This tells them which elements are present as well as which ionization state the elements are in (this also tells them the star's temperature). Ionized elements emit radiation at different wavelengths than neutral elements. Next, astronomers compare the relative strengths of the lines; this gives them an estimate of how much of each element is present. In this way, astronomers can determine the stellar composition from the star's spectrum.